Flexible metal clad laminate, production method thereof and apparatus for the method

ABSTRACT

An elongated flexible metal clad laminate formed of at least one metal layer and at least one plastic layer and having a smaller interlayer dimensional difference and excellent process-ability. A defect that a dimension of the metal layer is longer than a corresponding dimension of the plastic layer when they are compared to each other as discrete layers has been corrected by causing the metal layer to continually undergo compression plastic deformation in the form of the laminate and hence compressing the metal layer. A production method for the laminate and an apparatus for the method.

DESCRIPTION

1. Technical Field

This invention relates to an elongated flexible metal clad laminate(hereinafter abbreviated as "FMCL") which includes a layer of a functionplastic, e.g., a plastic excellent in heat resistance, electricalcharacteristics and mechanical characteristics such as a polyimide, alow dielectric-constant plastic such as polytetrafluoroethylene, aheat-sealable plastic such as polyethylene or a chemical resistantplastic such as polypropylene, and a metal layer having electricalconductivity, heat conductivity, electromagnetic shielding properties,gas barrier properties and the like, and which is useful in applicationfields such as the electrical, electronic, packaging and ornamentationfields. This invention is concerned with a flexible metal clad laminateformed of at least one metal layer and at least one plastic layer andhaving a smaller interlayer dimensional difference and excellentprocessability. A defect occurred in the step of lamination between themetal layer and plastic layer or a like step, that a dimension of themetal layer is longer than a corresponding dimension of the plasticlayer when they are compared to each other as discrete layers, has beensuccessfully corrected by causing the metal layer to continually undergocompression plastic deformation in the form of the laminate and hencecompressing the metal layer. This invention also relates to a productionmethod of the flexible metal clad laminate and to an apparatus forpractising the method.

2. Background Art

Flexible metal clad laminates (FMCLs) formed of at least one metal layerand at least one plastic layer are used as materials making full use ofcharacteristics of both a metal and a plastic, for example, as wrappingmaterials, substrates for flexible printed circuits, covering materialsfor electromagnetically-shielded wires and cables,electromagnetically-shielding films, etc.

It is necessary for these FMCLs that a suitable dimensional relationshipbe satisfied between a metal layer and its associated plastic layer inview of processing means and application purposes.

However, the production of FMCL is generally conducted by bonding ametal foil and a plastic film with an adhesive under heat, continuallyforming a plastic film over a metal foil, coating a metal foil with asolvent solution of a plastic polymer, or forming a metal on a plasticfilm by sputtering, vacuum evaporation or electroless plating. There istherefore a dimensional difference, in general, of about 0.1-5% betweenthe metal layer and plastic layer due to the difference in thecoefficient of thermal expansion, tensile strength, compressionstrength, the modulus of elasticity or percentage water absorptionbetween the metal and plastic, the occurrence of shrinkage upon dryingof the solvent, the occurrence of shrinkage upon curing. Although thetolerable dimensional difference varies from one application field toanother, the dimensional difference tends to fall outside of a desiredtolerable range in many instances. Those engaged in the present field ofart hence have difficulties in coping with inconvenience caused by sucha dimensional difference. For example, this dimensional difference isrequired not to exceed 0.3% in the field of flexible printed circuitboards and 0.05% in the field of TAB (tape automated bonding).

Although such a dimensional difference cannot be quantitatively measuredso long as FMCL is measured as is. Its measurement is however feasibleprovided that the elements, namely, the metal layer and plastic layerare separated from each other into discrete elements by a method notinducing a stress.

In many instances, the dimension of a plastic layer is generally smallerthan a suitable range, in other words, shorter compared to the dimensionof its associated metal layer.

A shorter plastic layer brings about adverse effects, which may bedivided into the following two types roughly.

a) FMCL is curled with the plastic layer being located inside. Extremedifficulties are therefore encountered upon its further working orprocessing in which FMCL must be worked or processed in a developedform, for example, upon stamping, cutting, patterning, superposing andbonding, and/or the like.

b) Upon printing a precise circuit pattern with an etching resist inkand then conducting etching to leave the metal layer partially astypified by a flexible printed circuit board (FPC), a dimensionaldifference occurs between a portion where the metal layer still remainsand another portion where the metal layer has been removed, so thatcreases are formed all over the laminate.

As a result, the relative positional relationship among individualpoints on the pattern varies so that the preciseness required for themounting of parts or for the establishment of a connection to anotherpattern is lost and its external appearance is also rendered lessattractive.

Where the dimension of the plastic layer is shorter beyond a certainspecific range compared to that of the associated metal layer, thelaminate is actually considered to have no practical utility.

Since there is generally no method capable of completely separating theindividual elements into discrete elements without applying anyadditional stress, the following method can be adopted by way of examplefor the measurement of such dimensional differences as a practicalseparation method capable of practically avoiding the occurrence offurther stress. Namely, the dimension of FMCL is measured as is. Thevalue thus measured is deemed to be equal to the dimension of the metallayer, namely, to the dimension of the plastic layer before etching.FMCL is thereafter subjected to etching with a reagent which does notgive influence to the plastic layer, so that the metal layer is removedto isolate the plastic layer. The dimension of the plastic layer ismeasured and is deemed to be the dimension of the plastic layer. Fromthese measurement data, the dimensional difference between both thelayers, which is equal to the difference obtained by subtracting thelength of the plastic layer after the etching from that of the plasticlayer before the etching, is determined.

In some instances, a variety of measures has heretofore been taken witha view toward eliminating the above-mentioned drawbacks which areconsidered to be fatal to FMCLs as products. No FMCL of satisfactoryproperties has however been completed yet.

As one example of techniques already known, there is a simplecurl-removing method in which as disclosed in Japanese Patent Laid-OpenNos. 22388/1984 and 22389/1984, a flexural plastic deformation oppositeto the curl is applied to a metal layer, in other words, the curledmetal layer is bent in a direction opposite to the curl, so that theresultant deformation is balanced with the stress responsible to thedevelopment of the curl due to the dimensional difference between themetal layer and its associated plastic layer, thereby hopefully reducingthe curl.

It is important to note that needless to say, the dimension of the metallayer itself is practically unchanged before and after the processing inthe above instance.

In FMCL processed by such a method, the curl caused as the adverseeffect (a) by the shorter dimension of its plastic layer has only beeneliminated tentatively. There is thus a drawback that the curl appearsagain immediately when FMCL has a thermal history. With respect to theadverse effect (b), namely, the development of creases upon etching, theabove method is also accompanied by a serious drawback that nosubstantive improvement has been made at all in the problem because thedimensional difference between the plastic layer and metal layer waspractically unchanged before and after the processing and remains aswas.

On the other hand, some attempts have been made with a view towardselectively stretching a plastic layer to make it close to the dimensionof its associated metal layer.

In Japanese Patent Laid-Open No. 23791/1981, it is attempted to make thedimension of a plastic layer close to that of its associated metal layerby causing the plastic layer to absorb a solvent and hence to swell tohave a longer length.

This method is however accompanied by a drawback that the plastic layershrinks again unavoidably because the thus-absorbed solvent escapes fromthe plastic layer when FMCL is exposed to a high temperature, forexample, to an atmosphere of 100° C. or higher or is left over for along period of time in the atmosphere. The above method is accompaniedby another problem that it is still very difficult to reduce thedimensional difference from the metal layer to a predetermined necessaryrange. The method of the present invention in which the dimension of ametal layer is reduced by compression plastic deformation, which isreasonable from the theoretical viewpoint and allows very smalldimensional changes along the passage of time, has not been found in anyprior art techniques.

DISCLOSURE OF THE INVENTION

An object of this invention is to provide an elongated FMCL whichincludes a function plastic composed of a heat-resistant plastic, lowdielectric-constant plastic, heat-sealable plastic or chemical resistantplastic or a combination thereof and a metal foil having variouscharacteristics, is useful in an application field such as theelectrical, electronic, packaging or ornamentation field, and hasexcellent processability and/or workability. A defect produced in thestep of their lamination or a similar step that the dimension of themetal layer is longer than that of the plastic layer when the metallayer and plastic layer can be separated from each other can becorrected by continually subjecting the metal layer to compressionplastic deformation and hence compressing the metal layer in the form ofthe laminate and the thus-corrected dimensional difference does notchange along the passage of time. Another object of this invention is toprovide a method for the production of the laminate. A further object ofthis invention is to provide an apparatus for practising the method.

When the dimension of a metal layer is longer than that of itsassociated plastic layer, their dimensional difference is reduced bycontinually subjecting the metal layer to compression plasticdeformation and hence reducing its dimension. For this purpose, theflexural stiffness of the metal layer may preferably be 20 g.cm orsmaller while that of the plastic layer may preferably be at least 1/500of the flexural rigidity of the metal layer.

Namely, the present invention can be practised efficiently by settingthe thickness of the metal layer to give a flexural rigidity of 20 g.cmor smaller and the thickness of the plastic layer to give a flexuralrigidity at least 1/500 of the flexural rigidity of the metal layerwhere the materials constituting FMCL have been chosen.

Since many of FMCLs useful in application fields such as the electrical,electronic, packaging and ornamentation fields satisfy theabove-described requirements in characteristics, they have significantadvantages such that they allow to reduce the dimensional differencesbetween their plastic layers and metal layers, permit a variety ofprocessing and/or working and in addition, provide processed or workedproducts having an improved processing or working accuracy, whereby asignificant contribution has been brought about to the industry.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a stress-strain curve of copper as a typicalexample of metal layers;

FIG. 2 is a diagram of a stress-strain curve of a polyimide as arepresentative example of plastics;

FIG. 3 is a vertical cross-section showing a state in which a metallayer of FMCL has developed a compression plastic deformation;

FIG. 4 is a vertical cross-section showing a state in which a metallayer of FMCL has developed a flexural deformation;

FIG. 5 is a plan view of FMCL as seen from the side of a plastic layerof FMCL and illustrates an operation in which FMCL is continually bent;

FIG. 6 and FIG. 7 are diagrams showing the direction of a compressionplastic deformation of a metal layer of FMCL;

FIG. 8(1) is a schematic plan view showing a situation in which FMCL iscontinually bent at a line angle, and FIG. 8(2) is a verticalcross-section along line A--A in FIG. 8(1) of the situation;

FIG. 9 is a schematic plan view of a situation in which the line angleof FIG. 8 has been set opposite;

FIGS. 10(a) to 10(i) depict in transverse cross-section blades ofvarious shapes;

FIGS. 11(1) and 11(2) are schematic plan view and vertical cross-sectionrespectively where guides are provided in accordance with thisinvention;

FIGS. 12(1) and 12(2) schematically show that the angle between a bladeand FMCL varies when a guide or guide roller useful in the practice ofthis invention is omitted;

FIG. 13 is a schematic illustration showing that FMCL on a blade ismeandering due to a thrust;

FIG. 14 is a schematic illustration of a thrust by a blade and anotherthrust by each guide roller;

FIG. 15 is a schematic illustration showing FMCL in a curled state;

FIG. 16 is a plan view showing the arrangement of reference points uponmeasurement of the dimensions of laminates in Examples and ComparativeExamples; and

FIG. 17 is a plan view showing the arrangement of reference points uponmeasurement of dimensions in Comparative Example 1.

In the drawings, there are illustrated FMCL 1, blade 2, metal layer 3,plastic layer 4, feeder or let-off guide roll 5, take-up machine orwinding guide roll 6, guide roller 7, guide roller 8, blade edge portion9, guide 10, guide 11, guide-in angle α, guide-out angle β, and lineangles θ,θ'.

BEST MODES FOR CARRYING OUT THE INVENTION

The most significant technical feature of the present invention residesin that upon reducing an interlayer dimensional difference in FMCL inwhich a metal layer is longer compared to its corresponding plasticlayer, the objective is achieved by concentrating attention on on themetal layer instead of the plastic layer and subjecting the metal layerto compression plastic deformation. When FMCL is used as a substrate fora printed circuit, the dimensional difference between its metal layerand plastic layer should preferably fall within 0.3%. In the case of afine-patterned circuit in particular, 0.1% or smaller is preferred with0.05% or smaller being especially preferred. The dimensional differenceshould be 0% ideally.

In order to reduce the dimensional difference between a metal layer andits associated plastic layer in FMCL where the metal layer is longerthan the plastic layer, it is necessary either to cause the plasticlayer to expand close to the dimension of the metal layer or to causethe metal layer to contract close to the dimension of the plastic layer.It is however considered to be absolutely impossible by those skilled inthe art to cause a thin metal layer of 100 μm or less, which maygenerally be called a "metal foil", to undergo a compression plasticdeformation. The method which has been practised usually to date is tostretch the plastic layer close to the dimension of the associated metallayer as mentioned in the background art. No satisfactory results havehowever been brought about from the method of stretching the plasticlayer close to the dimension of the associated metal layer. The presentinventors thoroughly studied properties of metal layers, properties ofplastic layers, etc. In complete contrast to the common knowledge ofthose skilled in the art and methods practised by them to date, it hasbeen found as the only method for obtaining FMCL with a reducedinterlayer dimensional difference that the metal layer is subjected tocompression plastic deformation so as to make the dimension of the metallayer close to that of the plastic layer. A method for applying acompression plastic deformation to the metal layer has also been found.As a result, the present invention has been completed.

First of all, the principle of subjecting a metal layer to compressionplastic deformation in the present invention will be described withreference to some of the drawings. Although a metal layer generally hasa greater modulus of elasticity compared to an associated plastic layer,plastic deformation amounts to a major proportion of the deformation.The stress-strain curve of a copper foil as a typical example of metallayer is shown in FIG. 1, while the stress-strain curve of a polyimidefilm as an illustrative plastic layer is depicted in FIG. 2. The rangesindicated by (a) and (b) in both FIG. 1 and FIG. 2 can be considered aselastic and plastic deformation ranges respectively. On the other hand,the range designated by (c) in FIG. 2 is a range in which a plasticexhibits a hysteresis deformation. The stress range in which an elasticdeformation is feasible is wide provided that the strain range featuringhysteresis is also considered to be an elastic range. Since the elasticrange of a plastic is far broader than that of a metal, it is possibleto establish a range, in which a plastic layer undergoes only an elasticdeformation without developing any plastic deformation in spite ofdevelopment of a plastic deformation in the metal layer, by suitablycontrolling the stresses to be applied to the metal layer and plasticlayer respectively. This range can be established only when the flexuralrigidity of the metal layer and that of the plastic layer satisfy acertain mutual relationship. In this invention, a stress in the aboverange is applied to both the metal layer and the plastic layer so as todevelop a compression plastic deformation of from 0.01% to 5% in themetal layer of FMCL.

In order to develop such a compression plastic deformation as describedabove in this invention, an operation is carried out as shown in FIG. 3.Namely, FIG. 3 is a drawing illustrating an operation for causing ametal layer to undergo a compression plastic deformation as seen in adirection transverse to FMCL. Of the metal layer and plastic layer bothforming FMCL, the metal layer to be subjected to compression plasticdeformation is continually bent in contact with a blade. As illustratedin FIG. 3, in FMCL bent on the blade 2, the inner metal layer 3 issubjected a compression stress while the outer plastic layer 4 issubjected to a tensile stress. The dimensional difference between themetal layer and the plastic layer in FMCL that the metal layer is longercompared to the plastic layer can be reduced by choosing a suitablestress here and subjecting the metal layer 3 and plastic layer 4 tocompression plastic deformation and tensile elastic deformation,respectively.

In order to have the metal layer and plastic layer of FMCL undergocompression plastic deformation and tensile elastic deformationrespectively as described above, the flexural rigidity of the metallayer may preferably be not greater than 20 g.cm but not smaller than1×10⁻⁸ g.cm, while that of the plastic layer may preferably be at least1/500 but at most 6×10⁹ of the flexural rigidity of the metal layer witha range of at least 1/100 but at most 1×10⁵ being more preferred.

When the flexural rigidity of the metal layer and that of the plasticlayer preferably, namely, are 20 g.cm or smaller and 1/500 of theflexural rigidity of the metal layer or greater respectively, the metallayer undergoes a plastic deformation as shown in FIG. 3 owing to thebalance in flexural rigidity between the metal layer and the plasticlayer, whereby a compression plastic deformation is developed throughoutthe layer.

On the other hand, a tensile stress is applied to the plastic layer. Theeffect of the tensile stress is however limited practically to thedevelopment of an elastic deformation so that no substantial changetakes place regarding the dimension of the plastic layer.

These results are combined together in this invention, so that only thecompression plastic deformation of the metal layer remains as apermanent contraction in FMCL processed as described above. As a result,FMCL itself undergoes a contraction and the dimensional differencebetween the metal layer and plastic layer is reduced accordingly,whereby the dimensional difference is removed practically andsubstantially. In other words, the metal layer is subjected tocompression plastic deformation to undergo a contraction, so that thedimension of the metal layer is reduced close to that of the plasticlayer and the dimensional difference is reduced correspondingly.

By controlling the flexural rigidity within the above-described range,it is possible to perform a control such that a greater stress isapplied to the metal layer to produce a greater compression plasticdeformation and a smaller tensile strain is exerted to the plasticlayer.

Where a plastic layer is longer than an associated metal layer in FMCLon the contrary, the dimensional difference between the plastic layerand metal layer in FMCL can also be removed practically andsubstantially by conducting a similar processing except that the plasticlayer is maintained in contact with the blade in contrast to theabove-described processing whereby the metal layer undergoes anexpanding plastic deformation and is hence stretched.

Incidentally, if the flexural rigidity of a metal layer exceeds 20 g.cm,the rigidity is so strong that the metal layer seems to undergo aflexural plastic deformation only and no compression deformation appearsto be feasible therefor. If the flexural rigidity of a plastic layer issmaller than 1/500 of that of the metal layer, the rigidity of the metallayer is too strong compared to the plastic layer so that the metallayer appears to undergo a flexural deformation alone.

This may be described more clearly. When the flexural rigidity of eachof the metal layer and plastic layer falls outside its correspondingrange specified in the present invention, both a tensile stress and acompression stress occur simultaneously in the metal layer asillustrated in FIG. 4 so that the metal layer undergoes a flexuraldeformation only. The dimensions of the metal layer have not thereforebeen changed when the metal layer is taken as a whole, whereby norelative dimensional change has taken place with respect to the plasticlayer. Accordingly, it does not appear to be feasible to reduce thedimensional difference between both the layers.

In the present invention, based on the above-described principle, astress is applied to FMCL and a metal layer is hence undergoes acompression plastic deformation. Described specifically, FMCL iscontinually bent under tension at a certain speed on a blade. FIG. 5 isa drawing as seen from the side of a plastic layer of FMCL, whichillustrates an operation in which FMCL is continually bent. Namely, whenFMCL 1 is fed under tension in a direction indicated by an arrow, forexample, by a means such as a let-off machine or guide roll and atake-up machine or take-up roller which are both arranged in a leveldifferent from the edge of the blade, FMCL 1 is continually bent on theblade 2 which is arranged in parallel with the width of FMCL and incontact with FMCL. The cross-section of FMCL at this time may beillustrated as shown in FIG. 3 and the metal layer 3 is caused toundergo a compression plastic deformation in accordance with theprinciple mentioned above. For illustration purposes, assume that theoperation of FIG. 5 is performed. Since the stresses exertedrespectively on the metal layer 3 and plastic layer 4 of FMCL 1 are in avertical direction relative to the blade, namely, in the travellingdirection (hereinafter called the "machine direction"), the direction ofcontraction of the metal layer is also the machine direction of FMCL 1.Practically no stress therefore occurs in the direction of the width(hereinafter called the "transverse direction") of FMCL 1, so that areduction in the dimensional difference between the metal layer andplastic layer constituting FMCL 1 can be achieved only in the machinedirection of FMCL 1. When there is a dimensional difference such thatthe metal layer is longer and the plastic layer is shorter only in themachine direction for a certain cause, for example, by a tension appliedin the machine direction in the step in which the metal layer andplastic layer have been laminated, FMCL having a small dimensionaldifference between its metal layer and plastic layer in all directionscan be obtained by reducing their dimensional difference in the machinedirection by the operation depicted in FIG. 5. A dimensional differencehowever exists in each of the machine and transverse directions betweenthe metal layer and plastic layer of FMCL in most instances.

In the case of such FMCL, the dimensional differences in desireddirections, namely, in all directions between the metal layer andplastic layer can be reduced by bending FMCL continually on a bladedisposed at a predetermined angle relative to the machine direction ofFMCL. FIG. 6 is a view as seen from the side of a plastic layer of FMCLand shows an operation in which FMCL is bent continually. In FIG. 6, theblade 2 is arranged at an angle indicated by θ relative to FMCL 1. Theangle indicated by θ means an angle over which the blade is deviatedfrom the transverse direction of FMCL as a standard line. Thecounterclockwise direction is indicated by a positive angle, while theclockwise direction is designated by a negative angle. These angles willhereinafter be called "line angles". When the operation depicted in FIG.6 is performed, stresses applied to the metal layer and plastic layer ofFMCL 1 have a vertical direction relative to the blade 2 (the directiona in FIG. 6), so that the direction in which the metal layer is causedto undergo a compression plastic deformation is also the direction a inFIG. 6. Since the compression plastic deformation produced in thedirection a in FIG. 6 can be resolved into the machine direction b andtransverse direction c of FMCL 1, the dimensional difference that themetal layer is longer than the plastic layer is reduced in both themachine direction and transverse direction.

Such a single operation is however incapable of developing a stress in adirection parallel to the blade 2, so that the dimensional difference inthat direction cannot be reduced. Dimensional differences in alldirections can therefore be reduced by conducting the operation shown inFIG. 7 subsequent to the operation of FIG. 6. Namely, when the lineangle θ is positive in the operation of FIG. 6, the blade is arranged togive a negative value to the line angle θ' in the operation of FIG. 7and a stress is then applied to FMCL 1. When the line angle θ isnegative, a stress is applied to FMCL 1 while setting the blade in sucha way that the line angle θ' has a positive value. In this manner, themetal layer is caused to undergo a compression plastic deformation,thereby making it possible to reduce in each direction the dimensionaldifference that the metal layer is longer compared to the plastic layer.It is possible to control the direction and degree of reduction of thedimensional difference by controlling the degree of compression plasticdeformation of the metal layer in each of the direction a in FIG. 6 andthe direction b in FIG. 7.

In order to reduce the above-described technical concept to practice, itis preferable to rely upon the following method. FIGS. 8(1) and 8(2) areschematic illustrations of an apparatus for actually applying a stressto FMCL 1 so as to reduce a dimensional difference that the metal layeris longer compared to the plastic layer, in which FIG. 8(1) is a topplan view whereas FIG. 8(2) is a vertical cross-section along line A--Ain FIG. 8(1). Namely, until FMCL 1 paid out from a roll 5 is taken up ona roll 6, the metal layer is bent on the blade 2 while maintained incontact with the blade 2 so that the metal layer is caused to undergo acompression plastic deformation to a degree of at least 0.01% but notgreater than 5%. By conducting this operation, it is possible toeffectively reduce the dimensional difference that the metal layer islonger compared to the plastic layer.

Incidentally, rolls 7,8 are provided respectively before and after theblade 2 in FIGS. 8(1) and 8(2). These rolls 7,8 are arranged to ensurethat FMCL 1 has suitable guide-in angle α and guide-out angle β at everypoint on the blade 2. Preferably, the rolls 7,8 are provided in parallelwith the blade 2. Although no particular limitation is imposed on theguide-in angle α and guide-out angle β, they may both preferably be atleast 10 degrees but not greater than 89 degrees in order to attain theadvantageous effects of this invention.

In order to ensure the compression plastic deformation of the metallayer upon performing the operation illustrated in FIG. 5 or FIG. 8, itis essential that FMCL 1 is continually bent on the blade 2 along theedge of the blade and is also allowed to pass by the edge againstresistance from the edge. For this purpose, FMCL is caused to travelwhile applying a tension to it by a conventional moving means, forexample, by using a take-up machine or take-up roller. According to aresult of a detailed study by the present inventors, this tension maypreferably be at least 10 g/cm but at most 10 kg/cm with at least 200g/cm being more preferred in many instances although no particular rangecan be mentioned sweepingly as it is dependent on the thickness, modulusof elasticity, etc. of each metal layer. When a rolled copper foil of 35μm thick is used by way of example, the desirable tension may range from200 g/cm to 1,000 g/cm. This tension is applied by controlling a driveapparatus for the take-up machine, for example, by either increasing ordecreasing the torque of an electric motor, or by providing a take-uproller before the take-up machine and controlling its drive torque.

Although no particular limitation is imposed on the speed at which FMCL1 is continually bent on the blade 2 in FIGS. 8(1) and 8(2), it ispreferable to perform the bending at a speed of from 0.2 m/min to 500m/min from the industrial standpoint.

In FIG. 8(1), the line angle θ may range from -80° to +80° with a rangeof from -60° to +60° being preferred.

In FIGS. 8(1) and 8(2), it is preferable to subject the metal layer tocompression plastic deformation at a temperature of at least 0° C. butnot higher than 200° C.

Compression plastic deformation of the metal layer in all directions isfeasible by applying a stress by a device as shown in FIG. 9 after theoperation of FIGS. 8(1) and 8(2). Namely, a similar operation as inFIGS. 8(1) and 8(2) except for a line angle θ' is conducted. Preferably,the line angle θ' in FIG. 9 is negative when the line angle θ in FIG.8(1) is positive but is positive when the line angle θ in FIG. 8(1) isnegative. When the operation is performed several times, positive lineangle and negative line angle may be alternated in such a way that anegative line angle is chosen after a positive angle, the positive angleis chosen again after the negative angle, and so on. As an alternative,the operation may be repeated a few times at a positive line angle andthen repeated a few times further at a negative angle.

By conducting each of the operations shown respectively in FIGS. 8(1)and 8(2) and FIG. 9 at least once in accordance with this invention andcausing the metal layer to undergo a compression plastic deformation toan extent of from 0.01% to 5%, the dimensional difference between themetal layer and plastic layer can be reduced thereby making it possibleto obtain FMCL which has a dimensional difference of ±0.3% between itsmetal layer and plastic layer and which is suitable for use in usualapplications. When the dimensional difference between the metal layerand plastic layer of FMCL that the metal layer is longer is reduced byconducting the operation of this invention, curling can also be reducedat the same time if FMCL is curled with the metal layer inside beforethe processing.

In the metal layer of FMCL in which the metal layer has been caused toundergo a compression plastic deformation by the operations illustratedin FIGS. 8(1) and 8(2) and FIG. 9 respectively, small dimensionalvariations may exist in the thicknesswise direction as a result of itsbending. In such a case, it is preferable to perform the operation shownin FIGS. 8(1) and 8(2) in such a way that FMCL 1 is bent with theplastic layer maintained in contact with the blade 2. This operationapplies a slight stress to the metal layer, so that dimensionalvariations in the thickness direction of the metal layer are reduced.

In this invention, various plastic materials and metal materials areusable depending on the end application. For example, as illustrativeheat-resistant plastics, there are polyimides, polyamide-imides,polyamides, polyethersulfones, polyether ether ketones, polyarylates,polyparabanic acid, polytetrafluoroethylene, polyethylene terephthalate,etc. They are often used as electrical and electronic materials. Copper,aluminum, nickel, brass and the like are frequently used as metal layersto be laminated. The plastic and metal are however not particularlylimited thereto. On the other hand, illustrative examples of lowdielectric-constant plastics may include resins such aspolyfluoroethylenes, e.g., polytetrafluoroethylene, polyphenylene oxide,polyimides, polyether sulfones, polyethylene, polypropylene andpolybutylene terephthalate. They are used primarily in electroniccircuit substrates which feature a low dielectric loss. Copper andaluminum are frequently used as metal layers to be laminated. Theplastic and metal are however not particularly limited thereto.Illustrative heat-sealable plastics are resins such as modifiedpolyethylenes, modified polypropylenes, modified ethylene-vinyl acetatecopolymers, etc. They are used primarily in packaging materials.Aluminum, gold and the like are frequently used as metal layers to belaminated. Of these applications, it is the field of electrical andelectronic materials such as electronic circuit substrates thatparticularly requires only a small dimensional difference between aplastic layer and its associated metal layer in the direction of theplane of the FMCL. The advantageous effects of the present invention canstill be brought about even if these metal layers are made of an alloyor composed of plural layers, so long as their flexural rigidity fallwithin the range specified above. Use of a copolymer, resin blend orresin alloy for the formation of these plastic layers, inclusion of aninorganic filler such as calcium, carbon fibers or ceramic, an inorganicfiller such as polytetrafluoroethylene and/or one or more of variousplasticizers and formation of these plastic layers by plural layers canstill bring about the advantageous effects of the present inventionprovided that the plastic layers satisfactorily fall within the aboveflexural rigidity range, and are hence embraced within the scope of thisinvention. Although no particular limitation is imposed on thelamination method useful in this invention for the production of FMCL,it is possible, for example, to cast a solution of a plastic or itsprecursor in a solvent on a metal layer and then to heat the solution toform a plastic layer on the metal layer; to form a plastic layer on ametal layer by melt extrusion; to laminate under heat adhesive-coatedplastic layer and metal layer; to form a metal layer on a plastic layerby sputtering or vacuum evaporation; to form a metal layer on a plasticlayer by electroless plating; or to form an additional metal layer,which has been formed on the metal layer by any one of the abovemethods, so as to provide a still thicker metal layer. It is alsopreferable to subject the metal layer or plastic layer to a surfacetreatment with an inorganic material and/or organic material so as toenhance the adhesion between the metal layer and plastic layer whichform FMCL.

In FMCL to which the present invention is directed, it is preferablethat the flexural rigidity of the metal layer is 20 g.cm or smaller andthe flexural rigidity of the plastic layer is at least 1/500 of that ofthe metal layer. Here, flexural rigidity is defined by the followingequation.

    D=Et.sup.3 /{12(1-ν.sup.2)}

wherein,

D: flexural rigidity (g.cm)

E: Young's modulus (g.cm²)

t: thickness (cm)

ν: Poisson's ratio (-)

The metal useful in the practice of this invention generally undergoes aplastic deformation under a stress, whereas the plastic employed in thepresent invention has viscoelastic properties. It is therefore difficultto measure their Young's moduli precisely. In this invention, flexuralrigidity is therefore specified in accordance with the above-describedflexural rigidity equation, using a so-called apparent Young's moduliunder a stress of at least 1 kg/mm² which is determined, for example, byconducting a tensile test of a metal layer or plastic layer alone at apredetermined pulling speed on a tensile testing machine and thenrelying upon a load-displacement chart or by measuring strain by astrain gauge.

The metal layer may be formed of plural metal layers or may be made ofan alloy so long its flexural rigidity does not exceed 20 g.cm. Thepreferable thickness of the metal layer may range from 0.05 μm to 100μm. On the other hand, the plastic layer may be formed of plural plasticlayers so long as its flexural rigidity is at least 1/500 of that of themetal layer. The thickness of the plastic layer may generally range from1 μm to 200 μm.

The dimensional difference between the metal layer and plastic layerforming FMCL can be determined in the following manner. Since therigidity of a metal is sufficiently greater than a plastic, the plasticlayer can be said to be elastically deformed by the metal layer in FMCLin which there is a dimensional difference between the metal layer andplastic layer. Upon removal of the metal layer from FMCL underconditions free of stress by etching or the like, the plastic layer isallowed to undergo an elastic deformation to restore its original shapeso that the original dimensions of the plastic layer itself can bedetermined. The relative dimensional difference between the metal layerand plastic layer (the percentage of shrinkage of the plastic layer) canthus be expressed by the following equation in this invention. ##EQU1##

Incidentally, the degree of the compression plastic deformation of themetal layer caused as a result of its bending on the blade is expressedas follows. ##EQU2##

In this invention, the blade to which FMCL is brought into contact maypreferably have, at the FMCL-contacting edge thereof, linearity ofaccuracy within ±1 mm in the transverse and/or vertical direction. Theterm "linearity" as used herein means that the FMCL-contacting portionhas linearity of the above-specific accuracy in the up-to-down directionand vice versa and/or the front-to-rear direction and vice versa. Thisaccuracy may preferably be within ±0.2 mm with ±0.05 mm beingparticularly preferred. Although the accuracy is ideally ±0.0 mm ofcourse, it is practically impossible to achieve it due to the accuracyof working. The blade is slightly deformed in the travelling directionof FMCL due to the tension of FMCL while the compression plasticdeformation of this invention is caused to occur. Preferably, thisdeformation should also be within 1 mm.

If the accuracy of linearity falls below ±1 mm, namely, the deviationfrom a straight line is greater than ±1 mm, the contact between FMCL andthe blade may probably become uneven on the order of microns so that thereduction of the dimensional difference may not be achieved uniformly.Where there are a more convex portion and a more concave portion in asingle piece of blade, an FMCL portion contacted to the convex portionhas a greater relative plastic deformation while another FMCL portioncontacted to the concave portion has a smaller relative plasticdeformation. The degree of compression plastic deformation thereforevaries within the same FMCL, thereby developing localized ruggedness orsurge which should not occur if the degree of plastic deformation wereuniform. In a certain extreme case, puckering or creases which lock likestreaks in the travelling direction may occur in FMCL after itsprocessing.

The width of FMCL is generally about 500 mm or so. When FMCL has a widthof 500 mm and the blade is arranged at the line angle of 45°, theFMCL-contacting portion of the blade is 708 mm long. At the line angleof 80°, the length increases to 2879 mm. It is by no means feasible todetermine the linearity of a blade of such a length, in other words, todetermine whether ruggedness of ±1 mm exists over a length of 500 mm ormore so long as the measurement is performed visually relying upon asquare or the like. In general, the measurement is feasible only when athree-dimensional measuring instrument whose measurable limit is on theorder of ±10 mm is used. In addition, linearity including variations incross-sectional shape can be measured by enlarging the cross-section ateach point in the longitudinal direction by means of a magnifyingprojector or the like. As has been discovered for the first time by thepresent inventors, totally unexpected differences in action take placeregarding the uniformity of a compression plastic deformation, effectsfor reducing an interlayer dimensional difference, existence ofnon-existence of puckering, etc., depending on linearity deviations ofan order as small as about θ1 mm or so, preferably, within about θ0.2mm, namely, of such a degree as not recognizable visually. This shouldbe extremely surprising.

A blade may have such a shape that the curvature of radius of an edgeportion, to which FMCL is brought into contact, as seen in alongitudinal cross-section thereof is smaller than 0.5 mm but greaterthan 0.001 mm, namely, greater than substantially zero radius ofcurvature. An radius of edge curvature of 0.5 mm or greater can apply aflexural plastic deformation to a metal layer but cannot apply anycompression plastic deformation to the metal layer, so that thedimensional difference cannot be reduced.

Any blade shape may be employed so long as the radius of edge curvaturefalls within the above range. Blades of various shapes may thus be used,including those having a trapezoidal, circular, oval, rectangular orsimilar vertical cross-section as viewed in the travelling direction ofFMCL.

Several examples of such a vertical cross-sectional blade shape areshown in FIGS. 10(a) to 10(i).

As depicted in the drawing, one or more FMCL-contacting edges may beprovided.

The material of the blade may be a metal, for example, iron steel,stainless steel, titanium, a titanium alloy or another alloy, a ceramicsuch as zirconia, glass or a composite material thereof. No particularlimitation is imposed thereon.

It is preferable to provide a guide right before and/or right after andin close proximity with the blade edge, for example, in order to controlthe dimensional difference between the metal layer and plastic layer ofFMCL or the contact pressure of FMCL to the blade, to control theguide-in angle or guide-out angle between the blade and FMCL, or tocontrol the tension to be exerted to FMCL upon its passage by the bladeedge.

FIG. 11(1) is a schematic plan view to be referred to upon descriptionof the method and apparatus of this invention, while FIG. 11(2) is avertical cross-section of the apparatus.

After FMCL 1 has advanced in a direction indicated by arrows and hasthen passed by the guide 10 while maintained in contact with the lowersurface of the guide 0, FMCL 1 passes over the edge portion 9 of theblade 2. FMCL 1 thereafter passes by the guide 11 while being maintainedin contact with a lower surface of the blade 2, whereby processing bythe blade 2 is completed.

The lower end faces of the guides 10,11 to which the upper side of FMCL1 is brought into contact, may preferably be in parallel with the edgeportion 9 of the blade 2 [see FIG. 11(1)] and define a contact surfacehaving good linearity like the edge portion 9. The radius of curvatureof the contact surface of each guide may preferably be at least 1 mmwith a range of from about 5 mm to about 100 mm or so being particularlypreferred for ensuring the effects of the processing.

The parallelism between the edge portion of the blade and each guide maypreferably be within θ1 mm, more preferably, θ0.2 mm over the entirelengths of their portions to which FMCL is brought into contact.

Each of the distances B and D in FIG. 11(2) may preferably be 300 mm orshorter with 100 mm or shorter being particularly preferred.

The lower limit of each of the distances B and D falls within a rangethat the blade is not in contact with the corresponding guide. The lowerlimit may be any value so long as FMCL is allowed to pass therebetween.A distance as small as 0.1 mm still permits the passage of FMCL.

Although the guides 10 and 11 are at the same level in FIG. 11(2) theymay be provided at different levels.

For the continuous processing of FMCL, let-off machine and windingmachine or guide rolls are arranged both before and after the bladerespectively. If the guides according to this invention are notprovided, the angle between the blade and FMCL varies along the width ofFMCL as indicated by α,α' in FIGS. 12(1) and 12(2). As a result, theeffects of the blade are not applied equally, so that the interlayerdimensional difference cannot be reduced substantially to zero andpuckering, ruggedness and meandering occur due to the uneven effects,thereby failing to obtain good FMCL. As a result of continuedtrial-and-error efforts against this very difficult obstacle, it wasfound surprisingly that unexpectedly good results of a uniform reductionof the dimensional difference over the entire surface of FMCL can beobtained when guides are provided at positions both before and after andin close proximity of the blade and in parallel with the blade edge andα,α' are set constant relative to FMCL and equal to each other, therebyleading to completion of the apparatus according to this invention.

It is preferable to provide a guide roller right before and/or rightafter, in close proximity with and in parallel with the blade edge inthis invention so as to achieve effective reduction of the interlayerdimensional difference between the metal layer and plastic layer, fineadjustment of contact pressure of FMCL to the blade, adjustment of thetension applied to to FMCL upon its passage by the blade edge, etc.

FIG. 8(1) is a schematic plan view illustrating method and apparatusaccording to this invention, while FIG. 8(2) is a vertical cross-sectionof the apparatus.

FMCL 1 advances in the direction indicated by the arrow. After passingby the guide roller 7 while being kept in contact with the lower facethereof, FMCL passes by the edge portion 9 of the blade 2. Thereafter,FMCL passes by the guide roller 8 while being maintained in contact withthe lower face of guide roller 8, whereby processing by the blade 2 hasbeen completed.

The lower end faces of the guide rollers 7,8, to which the upper side ofFMCL 1 is brought into contact, may preferably be in parallel with theedge portion 9 of the blade 2 and define a contact face having goodlinearity like the edge portion 9. The radius of curvature of thecontact surface of each guide roller may preferably be at least 1 mmwith a range of from about 5 mm to about 100 mm or so being particularlypreferred for the improvement of the effects of the processing. Theparallelism between the blade and each guide roller may preferably bewithin θ1 mm, more preferably, θ0.2 mm over the entire lengths of theirportions to which FMCL is brought into contact. The parallelism shouldbe 0 mm ideally.

Each of the distances B and D in FIG. 8(2) may preferably be 300 mm orshorter with 100 mm or shorter being particularly preferred. The lowerlimit of each of the distances falls within a range that the blade isnot in contact with the corresponding guide roller. The lower limit maybe any value so long as FMCL is allowed to pass therebetween. A distanceas small as 0.1 mm is still permissible.

As the material forming the entirety of each guide roller or its outerperipheral surface, it is possible to use any one of various materialssuch as metals, e.g., iron steel, stainless steel, titanium alloys oraluminum alloys, ceramics, glass, engineering plastics; or a compositematerial thereof.

Although the guide rollers 7 and 8 are at the same level in FIG. 8(2),they may be provided at different levels.

Effects, which may be brought about from the use of rolls as guides,will next be described.

When FMCL is caused to pass under tension while being maintained incontact with the blade, a friction occurs between the blade and FMCL. Inorder to reduce the interlayer dimensional difference or curling in alldirections of FMCL, the blade is arranged at the forementioned anglewith respect to the transverse direction of FMCL. In this case, a thrustis produced along the blade due to the friction between FMCL and theblade.

The present inventors have found that the omission of the guide rollersaccording to this invention results in movements of FMCL in thetransverse direction due to the thrust and puckering hence occurs onFMCL and in a severer case, the meandering becomes great and FMCL leavesthe blade to render the operation no longer feasible (see FIG. 13).

On the other hand, as illustrated in FIG. 14, sideward thrusts can beproduced in directions opposite to the above-described thrusts at theedges, namely, as indicated by arrows A and B by rotating the guiderollers. Namely, by controlling the revolutional speed of the guiderollers to a desired speed such that the combined thrust of thoseindicated by arrows A and B may cancel the thrust caused by the frictionbetween the blade and edge portion and indicated by arrow F, the extentof meandering of travelling FMCL can be reduced or completely avoided.

The speed of the outer peripheral surface of each of the guide rollers7,8 varies depending on the material of the surface of the roller andthat of the surface of FMCL, which is brought into contact with theroller. No particular limitation is hence imposed thereon. According toan investigation by the present inventors, it is however preferable fromthe standpoint of process control to control the speed to a level nothigher than the speed equal to the travelling speed of FMCL, namely, nothigher than the speed at which the outer peripheral speed of the rolleris equal to the travelling speed of FMCL and not higher than the speedat which the roller undergoes free rotation, so that the thrusts arecaused to cancel each other to prevent meandering. Although the speedalso varies depending on the thickness of FMCL and its guide-in andguide-out angles, an optimum speed can be chosen empirically with easefrom the above-described range.

The lower limit of the desirable speed may include a speed substantiallyequal to standstill. Good results may be obtained at a speed close tostandstill, although this depends on the kind of FMCL.

In addition to the above-described effects, primarily, themeandering-preventing effects, the guide rollers can also have the samefunction as the principal function of the aforementioned guides providedbefore and after the blade that α and α' in FIG. 12 are set equal toeach other.

Owing the the effects described above, FMCL does not undergo meanderingand is allowed to run stably thereby making it possible to obtain FMCLin which the dimensional difference is reduced evenly at all portions onthe entire area of FMCL.

Specific embodiments of the present invention will hereinafter bedescribed by the following Examples. They are however merely ofillustrative and should not be construed as limiting the scope of thisinvention.

EXAMPLE 1

A commercial polyamidic acid varnish ("Eupilex A", trade name; productof Ube Industries, Ltd.) was cast evenly on an elongated commercialelectrolytic copper layer ("3EC-III", trade name; product of MitsuiMining & Smelting Co., Ltd.), followed by drying under heat at 120° C.for 5 minutes and further at 180° C. for 6 minutes. The same polyamidicacid varnish was thereafter cast again on the coated surface to such anextent that the flexural rigidity of a polyimide film, which was to beformed subsequent to imidation, would be 0.1 g.cm or so. The lattervarnish was dried under heat at 120° C. for 5 minutes and further at180° C. for 6 minutes. The resultant product was finally heated for 20minutes in a nitrogen atmosphere of 330° C. having an oxygenconcentration of 0.5%, thereby obtaining an elongated FMCL having thepolyimide bonded directly to the copper layer. The thickness of thepolyimide was 30 μm at that time.

The FMCL was then slit with a 500 mm wide and then taken up on a windingroll.

When the FMCL was cut out in the form of a square of 200 mm×200 mm,curling having a radius of curvature of about 16 mm was developed withthe polyimide inside as shown in FIG. 15.

A 600 mm long sample was cut out from the FMCL and marks were placed onthe plastic layer as shown in FIG. 16. The distances between the marksA₁ -C₁, A₂ -C₂, A₃ -C₃, A₁ -A₃, B₁ -B₃ and C₁ -C₃ were 300.00 mmrespectively.

Next, after subjecting the FMCL to an etching treatment and henceremoving the copper layer, the above distances were measured again.Results are shown in the following table. Incidentally, the thickness ofthe polyimide layer after the removal of the copper layer was 30 μm. Inthe following table, MD indicates the advancing direction of the FMCLwhile TD designates its transverse direction.

    ______________________________________                                                   Distance Dimensional difference                                               after    between copper layer                                                 etching (mm)                                                                           and plastic layer (%)                                     ______________________________________                                                    A.sub.1 -C.sub.1                                                                       298.41   0.53                                            MD          A.sub.2 -C.sub.2                                                                       298.29   0.57                                                        A.sub.3 -C.sub.3                                                                       298.38   0.54                                                        A.sub.1 -A.sub.3                                                                       298.41   0.53                                            TD          B.sub.1 -B.sub.3                                                                       298.32   0.56                                                        C.sub.1 -C.sub.3                                                                       298.38   0.54                                            ______________________________________                                    

As described above, the dimension of the polyimide layer was shorter by0.53-0.57% than that of the copper layer.

The flexural rigidity of the copper layer employed in this Example afterthe heating step of the lamination procedure was 1.45 g.cm (thickness:35 μm; Young's apparent modulus under 3 kg/mm² tensile stress; 3600kg/mm² at 25θ and 5 mm/min pulling rate), namely, smaller than 20 g.cm.

Upon measurement of the polyimide film obtained above, its flexuralrigidity was 0.097 g.cm (thickness: 30 μm; Young's apparent modulusunder 1.5 kg/mm² tensile stress: 380 kg/mm² at 25θ and 5 mm/min pullingrate), namely, about 1/15 of the flexural rigidity of the copper layerand hence greater than 1/500 of the flexural rigidity of the copper. Theplastic layer was marked to set the distances between the marks A₁ -C₁,A₂ -C₂, A₃ -C₃, A₁ -A₃, B₁ -B₃ and C₁ -C₃ at 300.00 mm respectively.

Using a titanium alloy blade whose shape was as shown in FIG. 10(b) andwhose edge portion had a radius of curvature of 0.2 mm, the FMCL wasthen continuously bent once at each of line angles of +40° and -40°while maintaining the guide-in and guide-out angles at 50°, and thenonce at each of line angles of +40° and -40° while maintaining theguide-in and guide-out angles at 30°, namely, 4 times in total whileapplying a tension of 0.5 kg/cm and maintaining the copper layer incontact with the blade, thereby obtaining an FMCL whose copper layer hadbeen subjected to compression plastic deformation.

Although the thus-processed FMCL had mild curling of about 400 mm or soin terms of radius of curvature with the copper layer located inside, itwas substantially planar.

The above-marked portion of the FMCL whose dimensional differencereducing processing had been completed was cut out and the individualdistances were measured. The following results were obtained.

    ______________________________________                                                    Distance Percentage of plastic                                                after pro-                                                                             deformation of the                                                   cessing (mm)                                                                           copper layer                                             ______________________________________                                                    A.sub.1 -C.sub.1                                                                        298.68   0.44                                           MD          A.sub.2-C.sub.2                                                                         298.60   0.47                                                       A.sub.3 -C.sub.3                                                                        298.64   0.45                                                       A.sub.1 -A.sub.3                                                                        298.58   0.47                                           TD          B.sub.1 -B.sub.3                                                                        298.63   0.46                                                       C.sub.1 -C.sub.3                                                                        298.65   0.45                                           ______________________________________                                    

As is apparent from the above measurement results, the copper layerunderwent a compression plastic deformation and the dimension as FMCLshrunk by 0.44-0.47%. The resultant product is FMCL of this invention inwhich the copper layer as a metal layer has been subjected tocompression plastic deformation.

Next, in order to measure the dimensional difference between the copperlayer and plastic layer of the FMCL according to this invention, theFMCL was subjected to an etching treatment to remove the copper layer.Thereafter, the distances were measured again. The following resultswere obtained.

    ______________________________________                                                   Distance Dimensional difference                                               after    between copper layer                                                 etching (mm)                                                                           and plastic layer (%)                                     ______________________________________                                                    A.sub.1 -C.sub.1                                                                       298.41   0.09                                            MD          A.sub.2 -C.sub.2                                                                       298.35   0.08                                                        A.sub.3 -C.sub.3                                                                       298.40   0.08                                                        A.sub.1 -A.sub.3                                                                       298.36   0.07                                            TD          B.sub.1 -B.sub.3                                                                       298.38   0.08                                                        C.sub.1 -C.sub.3                                                                       298.40   0.08                                            ______________________________________                                    

As is apparent from the measurement results, excellent FMCL in which thecopper layer as a metal layer had been subjected to compression plasticdeformation and the dimensional difference between the copper layer andpolyimide layer is within 0.1% was successfully obtained in accordancewith this invention.

A fine patterned circuit was formed using the FMCL of this invention. Itwas possible to obtain an extremely good flexible printed circuit freeof puckering, waving, ruggedness or the like.

Comparative Example 1

An FMCL sample of 200 mm×200 mm was cut out from the untreated FMCLwhich had been obtained in Example 1 and had not been subjected tocompression plastic deformation. Marks were placed on the sample asshown in FIG. 17 in such a way that the distances of A-C, B-D, A-B andC-D were each 100.00 mm. With a view toward stretching the polyimidelayer of the FMCL, the FMCL was held at both MD end portions thereof atroom temperature and while applying a force of 100 kgf uniformly, theFMCL was maintained for 1 minute. Thereafter, the FMCL was held at bothTD end portions and while applying a force of 100 kgf uniformly, theFMCL was maintained for 1 minute. When the FMCL was taken out of thestretching machine, the FMCL contained pencil-like curves having aradius of curvature of 3 mm or smaller so that the curling had beenaggravated.

Upon measurement of the dimension of the FMCL, the following resultswere obtained.

    ______________________________________                                                  Distance after                                                                           Percent of stretch*                                                etching (mm)                                                                             of FMCL (%)                                              ______________________________________                                         ##STR1##    100.62 100.68                                                                              0.62 0.68                                            ##STR2##    100.67 100.65                                                                              0.67 0.65                                           ______________________________________                                         *Expressed by:                                                                ##STR3##                                                                 

Next, the FMCL was subjected to an etching treatment to remove thecopper layer and the above distances were measured again. Results aresummarized in the following table.

    ______________________________________                                                    Distance Dimensional difference                                               after    between copper layer                                                 etching (mm)                                                                           and plastic layer (%)                                    ______________________________________                                                    A-C        99.48    1.13                                          MD                                                                                       B-D        99.53    1.14                                                       A-B        99.52    1.14                                          TD                                                                                       C-D        99.50    1.14                                           ______________________________________                                    

Namely, the dimensional difference between the copper layer andpolyimide layer was increased on the contrary instead of being reduced.

Comparative Example 2

On an electrolytic copper foil which was of the same kind as thatemployed in Example and had the same flexural rigidity of 1.45.cm(thickness: 35 μm; Young's apparent modulus under 3 kg/mm² tensilestress: 3600 kg/mm² at 25° C. and 5 mm/min pulling rate), the polyamidicacid varnish of Example 1 was cast to such an extent that the flexuralrigidity of a polyimide layer to be formed subsequent to imidation wouldreach 2.6×10⁻³ g.cm.

The varnish was imidated under the same heating conditions as in Example1, thereby obtaining an FMCL which was composed of a copper layer and apolyimide layer.

A sample was cut out form the FMCL and was then subjected to etching toobtain the polyimide layer. Upon measurement of the polyimide layer, itsflexural rigidity was found to be 2.63×10⁻³ g.cm, which was about 1/551of the flexural rigidity of the copper layer (thickness: 9 μm; Young'sapparent modulus under 1.5 kg/mm² tensile stress: 380 kg/mm² at 25θ and5 mm/min pulling rate).

A 600 mm long sample was cut out from the FMCL and the dimensionaldifference between the copper layer and polyimide layer was measured inthe same manner as in Example 1. It was found to range from 0.53% to0.57%.

The FMCL was subjected to the same interlayer dimensional differencereducing processing as in Example 1. The thus-processed FMCL had mildcurling with the copper layer located inside.

The dimensional difference between both the layers in each of machineand transverse directions was measured in the same manner as describedabove. It was found to range from 0.52% to 0.59%, so that no reductionhad taken place in the dimensional difference. It was hence confirmedthat the copper layer as the metal layer of the FMCL had undergonesubstantially no compression plastic deformation.

The FMCL was then subjected to second interlayer dimensional differencereducing processing in the same manner as in Example 1. The interlayerdimensional difference was measured by the same measuring method as thatdescribed above. The difference was found to range from 0.53 to 0.58%and no reduction has yet occurred in the dimensional difference.

Using this FMCL, a wiring pattern was drawn by a usual method known perse in the art to fabricate a flexible printed circuit. Ruggedness andpuckering occurred, thereby failing to provide an acceptable flexibleprinted circuit.

Comparative Example 3

On a stainless steel foil having a flexural rigidity of 61.6 g.cm(thickness: 70 μm; Young's modulus: 19600 l kg/mm²), the polyamidic acidvarnish of Example 1 was cast to such an extent that the flexuralrigidity of a polyimide layer to be formed subsequent to imidation wouldreach 0.7 g.cm.

The varnish was imidated under the same heating conditions as in Example1, thereby obtaining an FMCL which was composed of the stainless steellayer and polyimide layer.

A sample was cut out form the FMCL and was then subjected to etching toobtain the polyimide film. Upon measurement of the polyimide film, itsflexural rigidity was found to be 0.70 g.cm, which was about 1/187.5 ofthe flexural rigidity of the stainless layer (thickness: 58 μm; Young'sapparent modulus under 1.5 kg/mm² tensile stress: 380 kg/mm² at 25θ and5 mm/min pulling rate).

A 600 mm long sample was cut out from the FMCL and the dimensionaldifference between the stainless steel layer and polyimide layer wasmeasured in the same manner as in Example 1. It was found to range from0.53% to 0.58%.

The dimensional difference between both the layers in each of themachine and transverse directions of the FMCL after its processing wasmeasured in the same manner as in that described in Example 1. It wasfound to range from 0.54% to 0.97%, so that no reduction had taken placein the dimensional difference. It was hence confirmed that the stainlesssteel layer as the metal layer of the FMCL had undergone substantiallyno compression plastic deformation.

Comparative Example 4

The unprocessed FMCL obtained in Example 1 was processed in the samemanner as in Example 1 except for the use of a blade having an edgeportion whose radius of curvature was 2.5 mm. As a result of theinterlayer dimensional difference between the copper layer and plasticlayer, it was found to be 0.55-0.6% in the machine direction and0.53-0.56% in the transverse direction. The dimensional difference hadhence not been reduced. It has been confirmed that the above processingcannot provide FMCL whose copper layer as a metal layer has beensubjected to compression plastic deformation.

EXAMPLE 2

A polyamide-polyamidic acid block copolymer was obtained by thefollowing procedures A, B and C.

A. Production of Polyamide Having Terminal Amino Groups

In a 1-l reactor fitted with a stirrer, an internal thermometer, adropping funned equipped with a pressure equalizer, and an inlet tube,6.84 g (0.0342 mole) of 4,4'-diaminodiphenyl ether was completelydissolved in 40 g of dry N,N-dimethylacetamide.

While cooling the internal temperature of the reactor at -5°-0° C. bymeans of a coolant jacket, a mixture of 2.46 g (0.0121 mole) ofisophthalic acid dichloride in a solid form and 2.46 g (0.0121 mole) ofterephthalic acid dichloride in a solid form was added little by littleto the solution in a nitrogen atmosphere.

After completion of the addition, the viscous. reaction mixture washeated to 10° C., at which it was stirred for 1 hour.

Next, a solution which had been prepared by diluting 3.09 (0.0532 mole)of propylene oxide with 6 g of dry N,N-dimethylacetamide was addeddropwise while maintaining the temperature of the reaction mixture at5°-10° C. After completion of the dropwise addition, the reactionmixture was stirred at 5°-10° C. for 1 hour to obtain a polyamide havingterminal amino groups and a calculated average molecular weight of1,000.

B. Production of Polyamidic Acid Having Acid Anhydride Terminals

In a similar reactor as in the procedure A, 27.1 g (0.124 mole) ofpyromellitic dianhydride was suspended in 41 g of dryN,N-dimethylacetamide.

A solution which had been prepared by dissolving 22.9 g (0.124 mole) of4,4'-diaminodiphenyl ether in 92 g of dry N,N-dimethylacetamide wasadded dropwise at 5°-20° C. in a nitrogen atmosphere.

The viscosity increased as the dropwise addition proceeded. In order toadjust the viscosity, 67 g of dry N,N-dimethylacetamide was added when75% of the amine solution had been added.

After completion of the dropwise addition, the reaction mixture wasstirred at 20°-25° C. for 1 hour to obtain polyamidic acid containingacid anhydride terminals and having a calculated average molecularweight of 5,000.

C. Production of Polyamide-polyamidic Acid Block Copolymer

A solution of the polyamide obtained by the procedure A and containingterminal amino groups was added at 15°-20° C. in a nitrogen atmosphereover about 30 minutes to a solution of the polyamidic acid obtained bythe procedure B and containing acid anhydride terminals.

Further, 89 g of N,N-dimehtylacetamide was added, followed by stirringat 20°-25° C. for 2 hours.

A viscous solution was obtained, which contained 15.0 wt. % of apolyamide-polyamidic acid block copolymer having an intrinsic viscosityof 1.62 as measured at 35° C. in the form of a 0.5 g/100 mlN,N-dimethylacetamide solution.

A solution of the polyamide-polyamidic acid copolymer obtained by theprocedure C was cast evenly on a rolled copper foil ("BHN-02", tradename; product of Nippon Mining Co., Ltd.; thickness: 35 μm). Afterdrying the solution under heat at 150° C. for 20 minutes, it was heatedfurther at 200° C. for 10 minutes and then at 300° C. for 10 minutes ina nitrogen atmosphere so that an FMCL having both a copper layer and apolyamide-imide layer was obtained.

The thickness of polyamide-imide layer of the thus-obtained FMCL was 35μm. The dimensional difference between the copper layer andpolyamide-imide layer was 0.54% in the machine direction and 0.52% inthe transverse direction.

Incidentally, the flexural rigidity of the copper layer used in thisExample after the heating step of the lamination procedure was 0.96 g.cm(thickness 35 μm; Young's modulus: 2400 kg/mm² ; testing method was thesame as that used in Example 1). The flexural rigidity of the plasticlayer was 0.30 g.cm (thickness 50 μm; Young's modulus: 250 kg/mm² ;testing method was the same as that used in Example 1).

The FMCL was continually bent under a tension of 500 g/cm at a speed of3 m/min on a blade made of a carbon tool steel, having a thickness of1.0 mm, equipped with an edge whose radius of curvature was 0.3 mm andcoated with a ceramic, while maintaining the copper layer in contactwith the edge portion of the blade. Here, the line angle was 30 degreeswhile the guide-in and guide-out angles were both 45 degrees. The FMCLwas then continually bent by the same operation as the above operationexcept that the line angle was changed to -30 degrees. Next, the FMCLwas continually bent by the same operation as the above operationsexcept that the guide-in and guide-out angles were both changed to 40degrees and the line angle was set at 30 degrees. Thereafter, the FMCLwas continually bent by the same operation as the above operationsexcept that the guide-in and guide-out angles were both set at 40degrees and the line angle was changed to -30 degrees.

The percentage of compression plastic deformation of the copper layer inthe FMCL obtained as described above was measured in the same manner asin Example 1. It was 0.46% in the machine direction and 0.44% in thetransverse direction. It was hence confirmed that the FMCL was an FMCLaccording to this invention in which the copper layer had been subjectedto compression plastic deformation. Further, the dimensional differencebetween the copper layer and polyamide-imide layer of the FMCL was 0.08%in both the machine and transverse directions. From this dimensionaldifference, the FMCL was also recognized to be a good FMCL whose copperlayer had been subjected to compression plastic deformation.

EXAMPLE 3

The interlayer dimensional difference of a commercial FMCL("ETCH-Å-FLEX", trade mark; product of Southwall Technologies Inc.),which had been obtained by laminating copper to 4 μm by a sputteringtechnique on a polyimide film having a thickness of 50 μm, was measuredby the same method as in Example 1. It was 0.14% in the machinedirection and 0.09% in the transverse direction. In both the directions,the copper layer was longer. When a sample of 200 mm×200 mm was cut out,curling having a radius of curvature of 30 mm occurred with the copperlayer positioned outside. The FMCL may be usable as a substrate for anordinary flexible printed circuit but is not suitable for TAB whichrequires a dimensional difference not greater than 0.05% between themetal layer and plastic layer. The flexural rigidity of the copper layerof the FMCL was 0.0025.cm (thickness: 4 μm; Young's apparent modulusunder 3 kg/mm² tensile stress: 4200 kg/mm²), which was not greater than20 g.cm. On the other hand, the flexural rigidity of the polyimide filmwas 0.36.cm (thickness: 50 μm; Young's apparent modulus under 1.5 kg/mm²tensile stress: 300 kg/mm²), which was about 1/0.07 of the flexuralrigidity of the copper layer, namely, greater than 1/500 of the flexuralrigidity of the copper layer.

Using a zirconia blade whose shape was as shown in FIG. 10(h) and whoseedge portion had a radius of curvature of 0.2 mm and a linearity within30 μm, the FMCL was then continuously bent once at each of line-anglesof +25° and -25° while maintaining the guide-in and guide-out angles at80°, and then once at each of line angles of +25° and -25° whilemaintaining the guide-in and guide-out angles at 50°, namely, 4 times intotal while applying a tension of 0.2 kg/cm and maintaining the copperlayer in contact with the blade, thereby obtaining an FMCL whose copperlayer had been subjected to compression plastic deformation.

Incidentally, as shown in FIGS. 8(1) and 8(2), guide rollers having aradius of curvature of 20 mm were provided both before and after theblade in such a way that the guide rollers are in parallel with theblade, the distances B and C were both 40 mm, and the parallelism withthe blade was 20 μm. The rotation of the guide rollers was controlled tomaintain the peripheral speed of the guide roller before the blade at 1m/min and that of the guide roller after the blade at 0.5 m/min.

During the processing, no meandering took place at all and the runningwas very stable, and the FMCL was absolutely free from phenomena such aswaving, ruggedness and puckering.

The FMCL obtained as described above was free of curling. When thedimensional difference between the polyimide layer and copper layer wasmeasured in the. same manner as in Example 1, it was 0.03-0.04% in themachine direction and also 0.03-0.04% in the transverse direction. Itwas hence possible to obtain very good FMCL which was substantially freeof dimensional difference and curling and was usable suitably for TABtoo.

EXAMPLE 4

One side of an elongated aluminum foil (material: 1070-0) having athickness of 25 μm was treated with vinyltriethoxysilane. Thethus-treated surface was coated with molten polyethylene, so that anFMCL having a polyethylene layer of 200μ thick was obtained. Thepercentage of shrinkage of the FMCL after its aluminum etching was 0.30%in the machine direction and 0.25% in the transverse direction.

Incidentally, the flexural rigidity of the aluminum layer employed inthis Example was 1.03 g.cm (thickness: 25 μm; Young's modulus: 7000kg/mm² ; testing method was the same as in Example 1) and that of theplastic layer was 1.59 g.cm (thickness: 200 μm; Young's modulus: 20kg/mm² ; testing method was the same as in Example 1).

On a zirconia ceramic blade having a thickness of 1.0 mm and equippedwith an edge whose radius of curvature was 0.15 mm, the FMCL wascontinually bent under a tension of 200 g/cm at a line angle of 35degrees, running speed of 30 m/min, a guide-in angle of 60 degrees and aguide-out angle of 60 degrees while maintaining the aluminum layer incontact with the blade edge. Thereafter, the FMCL was continually bentagain in the same manner as the aforementioned method except that theline angle was changed to -35 degrees. Both of the above operations wererepeated again.

Regarding the FMCL obtained as described above, the percentage ofcompression plastic deformation of its aluminum layer was measured inthe same manner as in Example 1. It was found to be 0.26% in the machinedirection and 0.20% in the transverse direction. On the other hand, thedimensional difference between the aluminum layer and polyethylene layerof the FMCL was 0.04% in the machine direction and 0.06% in thetransverse direction. The FMCL was hence found to be an FMCL in whichthe aluminum layer as a metal layer had been subjected to compressionplastic deformation and the dimensional stability was good. In addition,this state remained completely unchanged even after an elapsed time ofabout half a year.

EXAMPLE 5

FMCL "KL-1001(2510)" (trade name; product of Mitsui-Toatsu ChemicalsIncorporated), which was composed of a rolled copper foil of 35 μm thickand a "Kapton" (trade mark) film of 25 μm thick (product of DuPont-Toray Co., Ltd.) laminated on the copper foil with an acrylicadhesive interposed therebetween, had been laminated under heat andpressure in the lamination step of the copper layer and plastic layer.In certain lots of that step, the tension was poorly balanced so that agreater tension was applied in the machine direction. As a result, thecopper layer of the FMCL was stretched, and the dimensional differencebetween the copper layer and plastic layer was 0.35% in the machinedirection and 0.08% in the transverse direction.

Incidentally, the flexural rigidity of the copper layer employed in thisExample after having been processed through the heating step of thelamination procedure was 0.96 g.cm (thickness: 35 μm; Young's modulus:2400 kg/mm² ; testing method was the same as in Example 1) and that ofthe plastic layer was 0.146 g.cm (thickness and Young's modulus of the"Kapton" film: 25 μm and 300 kg/mm² ; thickness and Young's modulus ofthe adhesive layer: 25 μm and 60 kg/mm² ; testing method was the same asin Example 1).

The FMCL was continually bent under a tension of 300 g/cm at a speed of5 m/min on a high speed steel blade having a thickness of 1.0 mm and aradius of edge curvature of 0.4 mm while maintaining the copper layer incontact with the edge of the blade. Here, the line angle was 0 degreeand the guide-in and guide-out angles were both 60 degrees. Next, theFMCL was continually bent again in the same manner as theabove-described method except that the line angle was set at 10 degreesand the guide-in and guide-out angles were both changed to 50 degrees.The FMCL was continually bent further in the same manner as the methoddescribed right above except that the line angle was changed to -10degrees.

Regarding the FMCL obtained as described above, the percentage ofcompression plastic deformation of its copper layer was measured in thesame manner as in Example 1. It was 0.29% in the machine direction and0.03% in the transverse direction. Further, the dimensional differencebetween the copper layer and plastic layer in the FMCL was found to be0.07% in the machine direction and 0.05% in the transverse direction.The FMCL was hence conformed to be a good FMCL whose copper layer hadbeen subjected to compression plastic deformation.

We claim:
 1. A flexible metal clad laminate formed of at least oneplastic layer and at least one metal layer laminated together,characterized in that the flexural rigidity of the metal layer is atmost 20 g.cm, the flexural rigidity of the plastic layer is at least1/500 of the flexural rigidity of the metal layer, and the metal layerhas been subjected to compression plastic deformation in its planedirection to an extent of at least 0.01 percent but at most 5 percent.2. The laminate as claimed in claim 1 wherein when the metal layer isetched on its entire surface, the percentage of shrinkage of the plasticlayer is within ±0.3 percent based on the dimension of the laminatebefore the etching owing to the compression plastic deformation of themetal layer.
 3. The laminate as claimed in claim 1 wherein the thicknessof the metal layer is at least 0.05 μm but at most 100 μm.
 4. Thelaminate as claimed in claim 1 wherein the thickness of the plasticlayer is at least 1 μm but at most 200 μm.
 5. The laminate as claimed inclaim 1 wherein the metal layer is made of a member selected from thegroup consisting of copper, aluminum, nickel, gold, silver and an alloythereof, and the metal layer is a single layer or is composed of morethan two layers of different kinds of metal.
 6. The laminate as claimedin claim 1 wherein the plastic layer is made of a member selected fromthe group consisting of an aromatic polyamide, aliphatic polyimide,aromatic polyimide precursor, aliphatic polyimide precursor, aromaticpolyamide-imide, aliphatic polyamide-imide, aromatic polyamide,aliphatic polyamide, polyester, polyfluoroethylene, polyether sulfone,polyether ether ketone, polyethylene, polypropylene, polystyrene,polyvinyl chloride, a mixture of plural resin components including atleast one component of the aforementioned resin and copolymer of pluralresin components including at least one component of the aforementionedresin, and the plastic layer is a single layer or is composed of morethan two layers of different kinds of plastic.
 7. A method for reducingthe dimensional different between a metal layer and a plastic layer of aflexible metal clad laminate, said laminate being formed of at least oneplastic layer and at least one metal layer laminated together, theflexural rigidity of said metal layer being at most 20 g.cm and theflexural rigidity of said plastic layer being at least 1/500 of theflexural rigidity of the metal layer, said metal layer being longer thansaid plastic layer, characterized in that the flexible metal cladlaminate is caused to slide under a tension of greater than 200 g/cm incontact with a blade, said blade having a curvature of radius of an edgeportion, to which said metal layer is brought into contact, of smallerthan 0.5 mm whereby the laminate is continually bent so as to subjectthe metal layer to compression plastic deformation in its planedirection to an extent of at least 0.01 percent but at most 5 percent.8. The method as claimed in claim 7 wherein the accuracy of at least onevertical and transverse linearity of a portion of the blade, to whichthe flexible metal clad laminate is brought into contact, is within ±1mm in the lengthwise direction.
 9. The method as claimed in claim 7wherein the flexible metal clad laminate is pressed from the side of theplastic layer by a guide provided in parallel and close proximity to anedge of the blade, to which the flexible metal clad laminate is broughtinto contact, before or after passage of the laminate by the blade. 10.The method as claimed in claim 7 wherein the flexible metal cladlaminate is pressed from the side of the plastic layer by a guide rollerprovided in parallel and close proximity to an edge of the blade, towhich the flexible metal clad laminate is brought into contact, beforeor after passage of the laminate by the blade.
 11. The method as claimedin claim 10, wherein the rotation of the guide roller is controlled, interms of the circumferential speed thereof, at a desired speed nothigher than the speed equal to the travelling speed of the flexiblemetal clad laminate.
 12. An apparatus for reducing an interlayerdimensional different of a flexible metal clad laminate, said laminatebeing formed of at least one metal layer and at least one plastic layer,said metal layer being longer than said plastic layer thereby having theinterlayer dimensional difference therebetween, characterized in thatthe apparatus comprises a means for causing the flexible metal cladlaminate to travel under a tension of greater than 200 g/cm, a bladeprovided in such a way that the blade extends across the travelling pathof the laminate at an angle of from ±80° to -80° relative to thewidth-wise direction of the laminate and the metal layer of the laminateis brought into contact with the blade, said blade having a curvature ofradius of an edge portion, to which said metal layer is brought intocontact, of smaller than 0.5 mm, and a means for deflecting the laminateon the blade, whereby the flexible metal clad laminate is caused toslide under tension in contact with the blade and is hence continuallybent so as to subject the metal layer to compression plastic deformationin its plane direction to an extent of at least 0.01 percent but at most5 percent.
 13. The apparatus as claimed in claim 12 wherein the accuracyof linearity of a portion of the blade, to which the flexible metal cladlaminate is brought into contact, is within ±1 mm in at least one of thetransverse and vertical directions.
 14. The apparatus as claimed inclaim 12 further comprising a guide provided in parallel and closeproximity to an edge of the blade, to which the flexible metal cladlaminate is brought into contact, whereby before or after passage of thelaminate by the edge of the blade, the flexible metal clad laminate ispressed from the side of the plastic layer and is hence deflected by theblade.
 15. The apparatus as claimed in claim 12 further comprising aguide roller provided in parallel and close proximity to an edge of theblade, to which the flexible metal clad laminate is brought intocontact, whereby before or after passage of the laminate by the edge ofthe blade, the guide roller presses under rotation the flexible metalclad laminate from the side of the plastic layer and hence deflects theflexible metal clad laminate.
 16. The apparatus as claimed in claim 15wherein the rotation of the guide roller is controlled, in terms of thecircumferential speed thereof, at a desired speed not higher than thespeed equal to the travelling speed of the flexible metal clad laminate.